ABSTRACT Narrow‐bandgap semiconductors such as InSb combine high carrier mobility with favorable band topology, yet large lattice thermal conductivity and bipolar conduction at elevated temperatures have long capped their thermoelectric figure of merit. Here, we show that introducing reactive Co 2 O 3 nanoprecursors into an optimized In 1.01 Sb matrix triggers a spontaneous solid‐state reaction that simultaneously reconstructs the microstructure and modulates the electronic band structure. The reaction yields a CoSb x @In 2 O 3 @CoSb 3 core–shell heterostructure that is coherent with the surrounding matrix and thermodynamically stable under operating conditions. The acoustic‐impedance contrasts across the multilayered interfaces curtail the mean free path of low‐to‐mid‐frequency acoustic phonons, which are inaccessible to point‐defect scattering alone, and thereby suppress lattice thermal conductivity across the full acoustic spectrum. Co incorporation concurrently shifts the Fermi level toward the heavier secondary conduction valleys, raising the density‐of‐states effective mass and limiting bipolar excitation at high temperatures. Together, these effects yield a peak zT of ∼0.7 at 733 K and a projected single‐leg conversion efficiency of ∼5%. The approach provides an effective means of addressing these transport bottlenecks in other narrow‐gap thermoelectric systems.
Xin et al. (Thu,) studied this question.